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The development of an efficient and fast cryptosystem has become significant with the widespread use of internet and advancements in networking technology. A colour image encryption/decryption technique using image block generation from block-based Sequency-based Mapped Real Transform (SMRT) is introduced in this paper to achieve this goal. The encryption architecture uses a confusion-diffusion approach and begins by partitioning individual colour components of plain image into fixed-size blocks. This is followed by XOR operation between generated diffusion keys and the image blocks to achieve diffusion. SMRT of the diffused image block is found and confusion induced by image block operations. Encrypted image is obtained through inverse SMRT and compilation of encrypted colour components. The proposed cryptosystem demonstrates excellent features including high sensitivity, complex keystream, strong security, high encryption and decryption efficiency and simple structure.

A stream cipher generates long keystream to be XORed with plaintext to produce ciphertext. A stream cipher is said to be secure if the keystream that it produces is consistently random. One of the ways by which we can analyze stream ciphers is by testing randomness of the keystream. The statistical tests mainly try to find if any output keystream leaks any information about the secret key or the cipher’s internal state and also check the randomness of the keystream. We have applied these tests to different keystreams generated by ZUC, Espresso and Grain v1 stream ciphers to check for any weaknesses. We have also proposed four new statistical tests to analyze the internal state when the hamming weight of key and IV used is very high or low. Out of these four tests, Grain v1 fails the last test i.e. internal state correlation using high hamming weight IV.

Swapping a row with a row, a column with a column or row with a column are usual operations carried out to scramble the given input plain image. To introduce more complications for the potential hackers, a novel grayscale image encryption scheme using the variable length row-column swapping based scrambling (VLRCSBS) has been proposed in this study. Security of the cipher would be improved in this way. Two chaotic maps, Henon map and piecewise linear chaotic map (PWLCM) have been used. These maps provide three streams of random numbers. Two more streams of random numbers have been created by manipulating the two streams of Henon map. After the grayscale image is input, arbitrary row and column are selected from this image to realize the scrambling effects. A randomly selected vector of pixels from these selected rows and columns is swapped with each other for a number of times. If selected vectors of pixels intersect each other, then to avoid the loss of pixels data, an intersection filter (IF) has been employed to forgo the intersecting vectors of selected pixels from the row and column for swapping. Resultantly, the given image is confused abundantly. An Exclusive-OR(XOR) operation is conducted between the scrambled image and the keystream given by PWLCM to get the final encrypted image. In the previous studies, whole rows and whole columns were swapped with each other. Our study swapped randomly selected portions of the rows and columns for scrambling, which spawned more security. In order to introduce the plaintext sensitivity in the proposed cipher, the hash codes given by the SHA-256 hash function for each input image have been used to update the system parameters and the initial values of the chaotic systems. The value of information entropy attained through the proposed algorithm is 7.9975 which is very competitive. Besides, the simulation and the performance analyses with varied validation metrics express the robustness, defiance to the multifarious threats and potential for some real world application of the cipher.

Conventional cryptanalysis techniques necessitate an extensive analysis of non-linear functions defining the relationship of plain data, key, and corresponding cipher data. These functions have very high degree terms and make cryptanalysis work extremely difficult. The advent of deep learning algorithms along with the better and efficient computing resources has brought new opportunities to analyze cipher data in its raw form. The basic principle of designing a cipher is to introduce randomness into it, which means the absence of any patterns in cipher data. Due to this fact, the analysis of cipher data in its raw form becomes essential. Deep learning algorithms are different from conventional machine learning algorithms as the former directly work on raw data without any formal requirement of feature selection or feature extraction steps. With these facts and the assumption of the suitability of employing deep learning algorithms for cipher data, authors introduced a deep learning based method for finding biases in stream ciphers in the black-box analysis model. The proposed method has the objective to predict the occurrence of an output bit/byte at a specific location in the stream cipher generated keystream. The authors validate their method on stream cipher RC4 and its improved variant RC4A and discuss the results in detail. Further, the authors apply the method on two more stream ciphers namely Trivium and TRIAD. The proposed method can find bias in RC4 and shows the absence of this bias in its improved variant and other two ciphers. Focusing on RC4, the authors present a comparative analysis with some existing methods in terms of approach and observations and showed that their process is more straightforward and less complicated than the existing ones.

Subterranean 2.0 is a cipher suite that can be used for hashing, authenticated encryption, MAC computation, etc. It was designed by Daemen, Massolino, Mehrdad, and Rotella, and has been selected as a candidate in the second round of NIST’s lightweight cryptography standardization process. Subterranean 2.0 is a duplex-based construction and utilizes a single-round permutation in the duplex. It is the simplicity of the round function that makes it an attractive target of cryptanalysis. In this paper, we examine the single-round permutation in various phases of Subterranean 2.0 and specify three related attack scenarios that deserve further investigation: keystream biases in the keyed squeezing phase, state collisions in the keyed absorbing phase, and one-round differential analysis in the nonce-misuse setting. To facilitate cryptanalysis in the first two scenarios, we novelly propose a set of size-reduced toy versions of Subterranean 2.0: Subterranean-m. Then we make an observation for the first time on the resemblance between the non-linear layer in the round function of Subterranean 2.0 and SIMON’s round function. Inspired by the existing work on SIMON, we propose explicit formulas for computing the exact correlation of linear trails of Subterranean 2.0 and other ciphers utilizing similar non-linear operations. We then construct our models for searching trails to be used in the keystream bias evaluation and state collision attacks. Our results show that most instances of Subterranean-m are secure in the first two attack scenarios but there exist instances that are not. Further, we find a flaw in the designers’ reasoning of Subterranean 2.0’s linear bias but support the designers’ claim that there is no linear bias measurable from at most $$2^{96}$$ 2 96 data blocks. Due to the time-consuming search, the security of Subterranean 2.0 against the state collision attack in keyed modes still remains an open question. Finally, we observe that one-round differentials allow to recover state bits in the nonce-misuse setting. By proposing nested one-round differentials, we obtain a sufficient number of state bits, leading to a practical state recovery with only 20 repetitions of the nonce and 88 blocks of data. It is noted that our work does not threaten the security of Subterranean 2.0.

n this paper, we try to give a security evaluation of LIZARD stream cipher in regard to fault attacks, which, to the best of our knowledge, is the first fault analysis on LIZARD. We design a differential engine of LIZARD to track the differential trail of the keystreams. It is shown that the distributions of the keystream differences are heavily biased. Utilizing this characteristic, we propose an improved method to identify the fault location for LIZARD whose success probability approaches 1. Then we use the fault-free keystream and faulty keystreams to generate system of equations in internal state variables and solve it by SAT solver. The result shows that with 100 keystream bits, only 6 different faults are needed to recover the internal state. Finally, the comparison between LIZARD and Grain v1 shows that LIZARD is more resistable than Grain v1 in regard to fault attacks.

The key scheduling phase (KSP) of a stream cipher expands the uniformly chosen key (K) and initialization vector (IV) to a larger uniform looking state. The existence of non-randomness in KSP results in a non-randomness in the final keystream. In this paper, we observe a non-randomness in the KSP of the nonlinear feedback-based stream ciphers Grain-v1, Grain-128AEAD and Fountain-v1 of reduced round R. However, we could not exploit the non-randomness into an attack. It can be claimed that if the KSP generates a pseudorandom state, then the probability of generating a valid state T (i.e., in the range set of KSP function) of a cipher must be $$2^{-\delta }$$ , where $$\delta$$ is the length of padding bits. We show that a new valid state can be constructed by flipping a few bits of a given state of the cipher with a probability higher than $$2^{-\delta }$$ . We show that the non-randomness happens for $$R \le 129$$ , $$R\le 208$$ and $$R \le 193$$ rounds of KSP of Grain-v1, Grain-128AEAD, and Fountain-v1, respectively. Further, in the case of Grain-v1 and Grain-128AEAD, we also found non-randomness in some key, IV bits from the experiment.

This paper introduces an image encryption algorithm shorted as CITSPD, manipulated by circle index table scrambling and partition diffusion. Firstly, the circle index table is obtained through the generation, circle shift and transposition of the benchmark sequence. Secondly, the plain image is transformed into the wavelet coefficient and is then scrambled by the circle index table. Thirdly, the permutated image is disturbed by different noises and is further divided into four subsections. Finally, the forward and inverse partition diffusions are performed to the subsections for getting the cipher image. The main feature of this algorithm is that the robust chaos-based keystream and encryption process are highly sensitive to the plaintext, which will effectively resist against chosen-plaintext and known-plaintext attacks. In addition, the encryption scheme is free of noise attack since the inverse diffusion differs from the forward one. And the diffusion effect can be effectively enhanced by, as much as possible, increasing the small pixel value and decreasing the large pixel value. Experimental tests and security analyses are carried out to verify the advantages of the scheme.

is a stream cipher proposed by Ekdahl et al. at IACR ToSC 2019(3) with an objective to be deployed as the encryption primitive in 5G systems. The stream cipher offers 256-bit security and is ready for deployment in the post-quantum era, in which as a rule of thumb (due to Grover’s algorithm), quantum security will vary as the square root of the classical security parameters. The authors further report good software performance figures in systems supporting the instruction set. However, they only provide a theoretical analysis of the cipher’s hardware efficiency. In this paper, we aim to fill this gap. We look at the three most important metrics of hardware efficiency: area, speed and power/energy, and propose circuits that optimize each of these metrics and validate our results using three different standard cell libraries. The smallest circuit we propose occupies only around 4776 gate equivalents of silicon area. Furthermore, we also report implementations which consume as little as 12.7 pJ per 128 bits of keystream and operate at a throughput rate of more than 1 Tbps.

In this paper, we study the linear approximation of certain composition functions, with applications to SNOW 2.0 and SNOW 3G. We first propose an efficient algorithm to compute the linear approximation of certain composition functions with parallel operations, which has a linear-time complexity for any given mask tuple, and thus allows for a wide range of search for linear approximations. Naturally, we apply this algorithm to compute the linear approximations of the FSM of both SNOW 2.0 and SNOW 3G. For SNOW 2.0, we compute the linear approximation of the FSM for a wide range of linear masks, and obtain some results which enable us to slightly improve the data complexity of the known fast correlation attacks, by using multiple linear approximations and combining a small technique when applying the k-tree algorithm. For SNOW 3G, we make a careful search for the linear approximations of the FSM and obtain many mask tuples which yield high correlations. Using these linear approximations, we mount a fast correlation attack on SNOW 3G and recover the initial state of the LFSR with the total time complexity $$2^{222.33}$$ and memory complexity $$2^{221.74}$$ , given $$2^{220.74}$$ keystream words. Our attack does not pose a threat to the claimed 128-bit security of SNOW 3G.

In the participatory sensing framework, privacy protection of the Internet of Things (IoT) is very important. In this article, cryptography-based methods are utilized to protect participants’ privacy information in unsecured network channels for dynamic and real-time sensing tasks. The edge computing paradigm is introduced in the traditional participatory sensing framework to reduce network latency. Then, the Rivest Cipher 4 stream cipher and logistic mapping are combined to deal with the problems of participants’ limited resources and untruthful third-party platforms. Finally, the product algebra and logistic mapping are combined to deal with the problems of large numbers of participants’ access and poor randomness of keystream. Through extensive performance evaluation and comparison experiments on the real-world data, the effectiveness and adaptation of the proposed privacy protection based on stream cipher are verified. It could effectively solve the problem of poor network latency and improve the privacy protection level of IoT.

A novel image multi-encryption architecture based on hybrid keystream sequence generated by a single hyperchaotic system and Haar discrete wavelet transform (HDWT) is proposed. The architecture consists of a pre-cipher stage, first encryption operation, Haar discrete wavelet decomposition stage and a second encryption operation. In the pre-cipher stage, the algorithm applies two-level pixel position permutation of the image. The first encryption operation is accomplished by diffusing the pixel's numbers with keystream sequence generated by a sequence generator SG-1. The resulting cipher image is decomposed using two-dimensional HDWT decomposition technique. The decomposed image is further encrypted through operation between keystream sequence generated by sequence generator SG-2 and bytes of the decomposed image which are selected with the aid of a novel pseudo – 4 bit Boolean truth table-based byte selection mechanism. SG-1 and SG-2 are special cases of the hyperchaotic system and are evolved online by separately nullifying selected parameters of the hyperchaotic system. The novelty of the proposed architecture lies in the possibility of increasing the number of sequence generators, which can result in exponentially huge key space and fast encryption speed. A comprehensive complexity analysis of performance, security and robustness to attacks, confirmed the feasibility of the architecture.

Chaos-based encryption provides a practical way to protect the confidentiality of digital images nowadays. The increasing convenience ( e.g. , larger bandwidth) of data sharing stimulates the need for encrypting amounts of images in a fast manner. Yet most existing works aim to encrypt an image for each time. Although some parallel encryptions have been proposed, the speed is still far from satisfactory to proceed with the huge increasing number of images. This inspires us to consider another promising way, encrypting a batch of images parallelly for each time. We use maximum available number of threads in parallel computation for full use of processor resources. Considering the batch images as a shared resource, every thread competes with others to encrypt images in the shared resource in a preemptive manner for encryption. A classical permutation-diffusion architecture for chaos-based encryption is utilized for each thread, where logistic map and Lorenz system are used for generating keystream for permutation and diffusion, respectively. We make cryptographical analyses and perform experiments to confirm that the security is guaranteed. The results of efficiency tests demonstrate that the encryption speed is greatly improved compared with the state-of-art image encryption algorithms in parallel as well as serial modes.

WG-l ($$l=7,8,16,29$$) are the well-known Welch–Gong (WG) stream cipher family with different key length bits. The first version named WG (WG-29) stream cipher was introduced in eSTREAM project as a cipher suitable for hardware implementations. The other variants are proposed for different applications from RFID to fast communications. This paper presents an extensive fault analysis on the WG family. Fault attacks are powerful cryptanalytic tools to analyse cryptosystems, which are not vulnerable to other known cryptographic attacks. The security model used to analyse the WG ciphers applies random faults, which are allowed to be injected by an adversary. The adversary has no control over the fault locations and their values. For each WG-l stream cipher, an adversary needs to observe a specific number of keystream bits before they are able to recover the secret key. To recover the secret key of WG-8, the adversary needs to inject about six random faults and compute the secret key with data and time complexities about $$2^{15.78}$$ bits and $$2^{24}$$, respectively. The adversary can recover the secret key of WG-7, WG-16 and WG-29 ciphers with time complexities $$2^{22}$$, $$2^{42}$$ and $$2^{64}$$, respectively. The attacks have been verified experimentally.

For a stream cipher to be secure, the keystream generated by it should be uniformly random with parameter 1/2.Statistical tests check whether the given sequence follow a certain probability distribution. In this paper, we perform a detailed statistical analysis of various stream ciphers used in GSM 2G,3G, 4G and 5G communications. The sequences output by these ciphers are checked for randomness using the statistical tests defined by the NIST Test Suite. It should also be not possible to derive any information about secret key and the initial state ofthe cipher from the keystream. Therefore, additional statisticaltests based on properties like Correlation between Keystreamand Key, and Correlation between Keystream and IV are also performed. Performance analysis of the ciphers also has been done and the results tabulated. Almost all the ciphers pass thetests in the NIST test suite with 99% confidence level. For A5/3stream cipher, the correlation between the keystream and key is high and correlation between the keystream and IV is low when compared to other ciphers in the A5 family.

Capability architectures for memory safety have traditionally required expanding pointers and radically changing microarchitectural structures throughout processors, while only providing superficial hardening. We hence propose Cryptographic Capability Computing (C3) - the first memory safety mechanism that is stateless to avoid requiring extra metadata storage. C3 retains 64-bit pointer sizes providing legacy binary compatibility while imposing minimal touchpoints. Pointers are encrypted to unforgeably (within cryptographic bounds) reference each object. Data is encrypted even in caches and entangled with pointers for both spatial and temporal object-granular protection. Pointers become like unique keys for each allocation. C3 deploys a novel form of prediction for address translation that mitigates performance overheads even when addresses are partially encrypted. Use of a low-latency, low-area cipher from the NIST Lightweight Cryptography project avoids delaying loads by readying a data keystream by the time data is returned from the L1 cache. C3 is compatible with legacy binaries. Simulated performance overhead on SPEC CPU2006 is negligible with no memory overhead, which is a big leap forward compared to the overheads imposed by past memory safety approaches. C3 effectively replaces inefficient metadata with efficient cryptography.

A series of encryption algorithms called A5 is used to secure mobile telephone communications, producing a pseudo-random sequence that will be XORed with the data flowing in the air interface in order to secure them. These algorithms are essentially composed of shift registers with linear feedback, controlled generally by a function or with another register in order to favor the randomness character of the keystream generated. Evolutionary algorithms are bioinspired calculation methods, used much more to find optimal solutions. They are a family of algorithms whose principle is inspired by the theory of evolution, which consists in evolving a set of solutions to a problem given in order to find better results. This paper presents an improvement of the A5/1 algorithm by an evolutionary approach based on the use of Particle Swarm Optimization Algorithm (PSO) in order to limit some weaknesses and drawbacks found in the conventional A5/1 version, which have been cryptanalysed and several attacks have been published such as time memory trade off attacks, guess and determine attacks, biased birthday attack and the random subgraph attack. Our approach does not change the architecture of the A5/1 but it just serves to improve its shifting system by an evolutionary approach, which guarantees the quality of the keystream generated and makes it more complex and more secure so it can be be used in future mobile telecommunication networks.

HHL algorithm is a quantum algorithm for solving linear equation system. It can achieve an exponential improvement over the best classical algorithm. In this paper, we analyze the quantum security of Grain-128/Grain-128a stream cipher by using the HHL algorithm. Our algorithm is based on Chen and Gao’s research on solving nonlinear equation system in Chen et al. (Quantum algorithm for optimization and polynomial system solving over finite field and application to cryptanalysis, 2018. arXiv:1802.03856 ) and Chen et al. (Quantum algorithms for Boolean equation solving and quantum algebraic attack on cryptosystems, 2017. arXiv:1712.06239 ). Firstly, we build a nonlinear Boolean equation system by choosing any keystream. Then, the nonlinear equation system is transformed into a special linear equation system that can be solved with the HHL algorithm. Finally, we solve the system by the HHL quantum algorithm. Our attack requires $$ N > {2^8} $$ -bit keystream, and the complexity is $$O(2^{21} N^{3.5} \kappa ^2 e^\epsilon /\epsilon ^{0.5})$$ for Grain-128, and $$O(2^{21.5} N^{3.5} \kappa ^2 e^\epsilon /\epsilon ^{0.5})$$ for Grain-128a where $$\kappa $$ is the condition number of the matrix of the corresponding linear systems and $$\epsilon $$ is a given error bound. Then we give a toy example of Grain family to estimate $$\kappa $$ and briefly analyze the security of Grain-128/Grain-128a against HHL algorithm.

In this study, a novel asymmetric image encryption scheme based on the Rivest-Shamir-Adleman (RSA) algorithm and Arnold transformation is proposed. First, the asymmetric public key RSA algorithm is used to generate the initial values for a quantum logistic map. Second, the parameters of the Arnold map are calculated. Then, Arnold scrambling operation is performed on the plain image to achieve the rough hiding of image information. Third, each row and each column of the image are taken as different units respectively and then exclusive-OR (XOR) diffusion is applied. Finally, the generated keystream is used to perform an end-to-start cyclic modulo diffusion operation for all rows and columns to produce the final cipher image. In addition, the keystream is related to the plain image, which can enhance the ability to resist chosen plaintext attack and known plaintext attack. The test results also show that the proposed encryption algorithm has strong plain sensitivity and key sensitivity.

A differential fault attack framework for the Enocoro family of stream ciphers is presented. We only require that the attacker can reset the internal state and inject a random byte-fault, in a random register, during a known time period. For a single fault injection, we develop a differential clocking algorithm that computes a set of linear equations in the in- and output differences of the non-linear parts of the cipher and relates them to the differential keystream. The usage of these equations is two-fold. Firstly, one can determine those differentials that can be computed from the faulty keystream, and secondly they help to pin down the actual location and timing of the fault injection. Combining these results, each fault injection gives us information on specific small parts of the internal state. By encoding the information we gain from several fault injections using the weighted Horn clauses, we construct a guessing path that can be used to quickly retrieve the internal state using a suitable heuristic. Finally, we evaluate our framework with the ISO-standardized and CRYPTREC candidate recommended cipher Enocoro-128v2. Simulations show that, on average, the secret key can be retrieved within 20 min on a standard workstation using less than five fault injections.

Two new encryption algorithms for secure video transmission are proposed in this paper. The two algorithms employ different types of chaotic maps to generate the keystream for encrypting the video frames. Both algorithms involve a substitution step and a permutation step to achieve confusion and diffusion requirements. For efficient transmission, the video file is compressed before being encrypted. In the basic implementation of both algorithms, MPEG-2 standard is used for compression. However, the algorithms are shown to be compliant with other compression techniques. In the permutation step, the effect of the block size used in the shuffling process is examined. Smaller blocks result in increasing the processing time, while reducing both the correlation between adjacent pixels and the peak-signal-to noise ratio of an encrypted frame. The use of a Feistel structure is investigated to enhance security and its negative impact on the encryption time is demonstrated. The experimental results of the two proposed schemes confirm that they represent different tradeoffs between security and computational efficiency. Both schemes are sensitive to slight variations in the encryption key as apparent from the obtained differential measures. The conducted comparative study shows the competitiveness of the proposed schemes to existing schemes in literature.

Image encryption schemes can be vulnerable to a variety of cryptanalysis attacks. The use of key-dependent dynamic S-boxes has been shown to improve security. Threats of chosen-plaintext and chosen-ciphertext attacks still linger. In this paper, we present an efficient algorithm for constructing secure dynamic S-boxes derived from Henon map. We use the proposed dynamic S-box to construct an image encryption scheme that includes a novel combination of security features to resist chosen-plaintext and chosen-ciphertext attacks. Namely, a hash verification step at the end of the decryption procedure effectively thwarts chosen-ciphertext attacks. The hash also serves as an image dependent initialization for the keystream, which together with using an image dependent S-box resist known-plaintext attacks. Furthermore, encryption keys are protected against cryptanalysis using elliptic curve cryptography (ECC).Therefore, the recovery of secret keys is as hard as the elliptic curve discrete logarithm problem even in the unlikely case of the recovery of the temporary S-box or keystream. Our evaluation of the proposed image encryption scheme reveals that it achieves a higher security standard than existing techniques. Moreover, the proposed scheme is computationally efficient with encryption throughput approaching 60 MB/s.

A method is proposed for evaluation of the security of SNOW 2.0-like ciphers against correlation attacks that are generated by analogy with the well-known attacks on the SNOW 2.0 cipher. Unlike the available methods, the proposed one focuses on proving the security and allows obtaining lower bounds of effectiveness of attacks of the considered class directly by the parameters of stream ciphers components in the same way as it proves the security of block ciphers against linear cryptanalysis. Application of the method to SNOW 2.0 and Strumok ciphers shows that any of the considered correlation attacks on them over the field of order 256 has an average time complexity no less than 2146 . 20 and 2249. 40 , respectively, and requires no less than 2142.77 and 2249. 38 keystream symbols, respectively.

The $\mathsf {Rasta}$ cipher, proposed by Dobraunig et al. (CRYPTO 2018), is an HE-friendly cipher enjoying the fewest ANDs per bit and the lowest ANDdepth among the existing ciphers. A novel feature of $\mathsf {Rasta}$ is that its affine layers are freshly and randomly generated for every encryption. In this paper, we propose a new variant of $\mathsf {Rasta}$ , dubbed $\mathsf {Masta}$ . Similarly to $\mathsf {Rasta}$ , $\mathsf {Masta}$ takes as input a (master) secret key and a nonce, and generates a keystream block for each counter. On the other hand, $\mathsf {Masta}$ has two main differences from $\mathsf {Rasta}$ : $\mathsf {Masta}$ uses modular arithmetic to support HE schemes over a non-binary plaintext space, and it uses a smaller number of random bits in the affine layers by defining them with finite field multiplication. In this way, $\mathsf {Masta}$ outperforms $\mathsf {Rasta}$ in a transciphering framework with $\mathsf {BGV}/ \mathsf {FV}$ -style HE schemes. Our implementation shows that $\mathsf {Masta}$ is 505 to 592 times faster in terms of the throughput on the client-side, while 4792 to 6986 times faster on the server-side.

In this paper, we study the security of a compressed sensing (CS) based cryptosystem called a sparse one-time sensing (S-OTS) cryptosystem, which encrypts a plaintext with a sparse measurement matrix. To construct the secret matrix and renew it at each encryption, a bipolar keystream and a random permutation pattern are employed as cryptographic primitives, which can be obtained by a keystream generator of stream ciphers. With a small number of nonzero elements in the measurement matrix, the S-OTS cryptosystem achieves efficient CS encryption in terms of memory and computational cost. In security analysis, we show that the S-OTS cryptosystem can be indistinguishable as long as each plaintext has constant energy, which formalizes computational security against ciphertext only attacks (COA). In addition, we consider a chosen plaintext attack (CPA) against the S-OTS cryptosystem, which consists of two sequential stages, keystream and key recovery attacks. Against keystream recovery under CPA, we demonstrate that the S-OTS cryptosystem can be secure with overwhelmingly high probability, as an adversary needs to distinguish a prohibitively large number of candidate keystreams. Finally, we conduct an information-theoretic analysis to show that the S-OTS cryptosystem can be resistant against key recovery under CPA by guaranteeing that the probability of success is extremely low. In conclusion, the S-OTS cryptosystem can be computationally secure against COA and the two-stage CPA, while providing efficiency in CS encryption.

Non-linear filtering generators, as a well-known family of stream ciphers, employ a filtering function F : GF ( 2 ) n → GF ( 2 ) m to process the secret state bits and thus outputs binary keystream blocks of length m. In this study, the authors extend the framework of a generic cryptanalytic method applicable to non-linear filtering generators called generalised filter state guessing attacks (GFSGA), introduced as a generalisation of the filter state guessing attack method, by applying a variable sampling of the keystream bits in order to retrieve as much information about the secret state bits as possible. Two different modes that use a variable sampling of keystream blocks are presented and it is shown that in many cases these modes may outperform the standard GFSGA mode. They also demonstrate the possibility of employing GFSGA-like attacks to other design strategies such as non-linear feedback shift register-based ciphers (Grain family for instance). It is also indicated that the tap positions of Grain-128 are not chosen optimally with respect to this generic cryptanalytic method and provide a better selection of taps that gives higher resistance to GFSGA-like attacks.

In recent years, with the rapid development of chaotic technology, many chaotic image cryptosystems based on pixel/bit-level techniques have been investigated. However, the drawbacks of a cryptosystem are as follows: (1) the security and efficiency are merely based on an investigation into standard test images and are not suitable for certain unique images in which the existence of “1s” or “0s” is significant; (2) the processing of bits requires more chaotic variables that elevate the computational complexity; (3) computational redundancy occurs when encrypting certain unique images. The first comprehensive analysis of different types of existing bit/pixel-level permutation techniques is carried out to show the inapplicability of such algorithms for popular cloud computing technology. To address the aforementioned security pitfalls of the state-of-the-art approaches and promote efficiency, an improved scrambling algorithm (ISA) and a reverse diffusion based on a dynamic keystream allocation strategy (DKAS) have been proposed. The present study adopts a spatiotemporal mixed linear-nonlinear coupling with the logistic-sine system (SMLNLC-LSS) for chaotic orbit generation. This system uses coveted cryptographic properties contrasted with the existing chaotic systems. The employed strategies such as ISA and reverse diffusion strongly enhance the relationship between the plaintext and encryption process to fortify the breaking of the proposed algorithm under known attacks. Because the ISA and DKAS mechanism share the same keystream, the efficiency of the proposed algorithm is effectively improved. Extensive security evaluation methods such as statistical, sensibility, visual-assessment, and efficiency analyses were imposed on the proposed methodology. The corresponding results accentuate the efficiency of the image cryptosystem while maintaining the superior security performance provided by the assurance of the desirable cryptographic properties.

Privacy and confidentiality can be secured by using cryptography. Thus, one needs to be sure that the ciphers being employed are secure and resistant to cryptanalysis. In the paper, a new state recovery attack on the RC4+ stream cipher is described. This attack is a plaintext attack where having both the plaintext and ciphertext the attacker can calculate the keystream what leads to revealing the internal state of the cipher. The presented approach is based on a Tabu Search with different types of neighbourhood and two types of aspiration proposed and considered. It requires checking 2 50 possible internal states on average in order to find the correct state. This is the best-known attack on RC4+. The other attacks that are known to date are a distinguishing attack and a differential fault analysis but only proposed approach can lead to revealing the internal state of RC4+ after checking so little permutations on average.

Long Term Evolution (LTE) of (Universal Mobile Telecommunication System) is one of the modern steps in series of mobile telecommunications systems. That appears to be a strong technology that meets the requirements of fourth-generation (4G) mobile networks and supports authentication and encryption mechanisms between User Equipment (UE) and Message Management Entity (MME). This paper provides an overview of the three most important algorithms that are considered the heart of LTE cryptographic algorithms (SNOW3G, AES, and ZUC) and a comparison between cipher key length and initial vector length to generate keystream depending on the structure used for each algorithm as each algorithm has a time of complexity and space of complexity that differs from the other security algorithm.

Polar codes have been shown to provide an effective mechanism for achieving physical-layer security over various wiretap channels. A majority of these schemes require channel state information (CSI) at the encoder for both intended receivers and eavesdroppers. In this paper, we consider a polar coding scheme for secrecy over a Gaussian wiretap channel when no CSI is available. We show that the availability of a shared keystream between friendly parties allows polar codes to be used for both secure and reliable communications, even when the eavesdropper knows a large fraction of the keystream. The scheme relies on a predetermined strategy for partitioning the bits to be encoded into a set of frozen bits and a set of information bits. The frozen bits are filled with bits from the keystream, and we evaluate the security gap when the cyclic redundancy check-aided successive cancellation list decoder is used at both receivers in the wiretap channel model.